Gas turbine engines generally include a core engine powering a turbine to rotate one or more fan or propeller blade. One type of gas turbine engine, known as an “open rotor” design, operates similarly to a conventional turbofan and turboprop designs, but with fuel efficiency that is superior to both. A turbofan engine operates on the principle that a central gas turbine core drives a bypass fan, the fan being located at a radial location between a nacelle of the engine and the engine core. However, in an open rotor design, a “bypass” propeller is mounted outside of an engine's nacelle. This permits the propeller to act on larger volumes of air and generate more thrust than with conventional turbofan engine. In some open rotor engines, the “bypass” propeller includes two counter-rotating rotor assemblies, each rotor assembly carrying an array of propeller blades located outside the engine nacelle.
A pitch control system may be attached to the propellers in order to alter the propellers' pitch angle according to desired flight characteristics. Optimum performance requires such systems to have a high-degree of accuracy. However, the desired pitch range may differ according to the ambient conditions or determined operation state. As a result, the pitch or pitch range which is suitable for one condition, may be wholly unsuitable for another. As a result, an ideal propeller pitch for one condition may lead to catastrophic failure in another. Existing systems often lack fail-safes or additional features that limit propeller pitch from inadvertently entering into a dangerous or non-ideal range.
Accordingly, improved pitch control systems and methods are desired. In particular, pitch control systems and methods for gas turbine engines that selectively limit the pitch angle may be beneficial.